1. Field of the Invention
The invention relates to a dual mode mobile telephone apparatus which is applicable to a mobile station in a mobile radio communication system. More particularly, the present invention relates to a dual mode mobile telephone apparatus having a plurality of different communication modes, such as an analog radio channel and a digital radio channel, which is able to communicate using either mode.
2. Description of the Prior Art
FIG. 14 shows a block diagram of the conventional dual mode mobile telephone apparatus which is applied to a mobile station in the mobile radio communication system. In FIG. 14, a control portion 1 consists of a CPU 1a, a random access memory RAM 1b, a read only memory ROM 1c, a non-volatile memory NVM 1d and an input/output port I/O 1e. The control portion 1 controls all portions of the dual mode mobile telephone apparatus. An analog mode transmitting/receiving portion 2 is controlled by the control portion 1 and transmits or receives an analog signal between the mobile station and the base station via the network . A digital mode transmitting/receiving portion 3 is also controlled by the control portion 1 and transmits or receives the digital signal between the mobile station and the base station via the network. An operation portion 4 has a plurality of function keys and sends the information to the control portion 1. A call mode store portion 11 stores a call mode which assigns, for example, the analog mode or the digital mode of the dual mode for the mobile radio communication system. The call mode portion 11 is stored, for example, in the NVM 1d in the control portion 1. A response signal generating portion 12 generates a response signal which is sent back to the base station according to the calling signal for the station from the base station. The response signal includes the calling signal stored in the call mode store portion 11. The response signal generating portion 12 may be constructed from, for example, the software functions of the CPU 1a in the control portion 1.
The operation of the above conventional art is explained hereinafter using FIG. 14 and FIG. 12.
FIG. 12 is a time chart which explains the signal flow between the base station and dual mode mobile station (DMMS).
When the power source is switched on, the control portion 1 searches, for example, an analog control channel. When the control portion 1 finds the analog channel, an order signal such as a system information and calling signal is transmitted or received using the analog channel. This state is called "idle state".
Firstly in the idle state, suppose that a calling signal is transmitted from the base station to the dual mode mobile telephone apparatus. An assigned dual mode mobile telephone apparatus sends back the response signal to the base station, which is generated in the response signal generating portion 12 of the control portion 1. The response signal indicates a communication mode in which the dual mode mobile telephone apparatus can communicate with the base station.
FIG. 13 shows a construction of a call bit. The call mode is consisted of three bits, they are b.sub.0 bit which indicates an analog channel, b.sub.1 bit which indicates a full rate digital channel, b.sub.2 bit which indicates a half rate digital channel. In the dual mode mobile telephone apparatus which can be available both analog channel and digital channel, the call mode is expressed by (b.sub.2, b.sub.1, b.sub.0) bits. And the combination of the three bits fixed as "110", "010" or "100" in the call mode store portion 11 . In the private analog mobile station, "000" is allocated to a call mode which can be available only analog mode.
When the calling signal is inputted to the dual mode mobile telephone apparatus, the response signal including, for example, a digital signal "110" indicating availability to communicate with both analog and digital modes, is returned back to the base station. The base station analyzes the response signal, and recognizes that the dual mode mobile telephone apparatus is available to both analog and digital modes. Then the base station sends the assignment signal which assigns either the analog mode or the digital mode. The selection of the call mode is decided by the base station.
The dual mode mobile telephone apparatus selects the operation mode according to the assignment signal from the base station. Then, when the dual mode mobile telephone apparatus receives the alert signal from the base station, the dual mode mobile telephone apparatus lets the user know the incoming signal by the ringing tone or the display. Then, when the user takes the hook off or makes the corresponding operation from the keyboard, the control portion 1 sends the connection signal to the base station. The line then becomes the communication channel between the DMMS and the base station. Similar conventional dual mode mobile telephone apparatus is disclosed in Japanese laid-open patent publication (Tokkai-hei 1-282929).
As discussed above, this apparatus is designed so that the selection of the call mode is decided only by the base station. Therefore, when the two modes are different with respect to the service type and/or the call charges, the user can not select the call mode which he likes, even if the user wants one of the modes.
It is accordingly a primary object of the present invention to provide a dual mode mobile telephone apparatus in which the user can select one of the modes at any time, even during the communication state.